Semiconducting metal oxides have been used for chemical sensing.
Indium oxide, or In2O3 has been found to have advantageous sensitivities to certain gases, such as O3, Cl2, NO2, NH3, CO and H2 when used as a sensor. Sensors of this type may be characterized in terms of their sensitivity. The sensitivity of a sensor is defined as the ratio of the resistance of the sensor after exposure, divided by the resistance of the sensor prior to exposure. The sensitivity of indium oxide thin-film devices may be around 58% for diluted NO2 gas, with a response time of several minutes.
Thin-film sensing devices have inherent limitations. These devices may have a limited maximum sensitivity based on the limited surface to volume ratio for the thin films. Moreover, many of these thin-film devices are intended to be operated at high temperatures, for example, 200 to 600° C. These high temperatures may enhance the chemical reactivity between the sensor materials and the surrounding gases. However, this high temperature requirement may be inconvenient for many applications.